The aim of this proposal is to resolve, if possible, the discrepancies between biophysical and biochemical evidence of repair and ultimate survival in irradiated cells. Because of its unique role in controlling cell function, many recent studies have focused on DNA and the results of alkaline sucrose gradient analysis of DNA from irradiatd cells. These studies have been interpreted to indicate that there is extensive repair of single strand breaks. Recent experiments in our laboratory suggest that alternative mechanisms may play an important role. Because of the close association between DNA and the plasma membrane in E. coli, preliminary studies of bacterial cell membrane changes after irradiation will be extended. Studies on the effect of radiation on cell membranes may have relevance to the clinical treatment of malignant disease in that they may provide a better rationale for the use of combined radiation and chemotherapy.